The present invention relates to a waste heat utilization device for an internal combustion engine, in particular of a motor vehicle having a waste heat utilization circuit. The invention further relates to an associated operating method.
A waste heat utilization device is known from JP 2006-349211 A which operates according to the Rankine cyclic process or according to the Rankine Clausius process. This type of waste heat utilization device includes a waste heat utilization circuit in which a working medium circulates, a conveying device, situated in the waste heat utilization circuit for conveying the working medium against a high pressure, an evaporator situated in the waste heat utilization circuit downstream of the conveying device, for evaporating the working medium by utilizing waste heat from the internal combustion engine, expansion machine, situated in the waste heat utilization circuit downstream of the evaporator for expanding the working medium to a low pressure, and a condenser, situated in the waste heat utilization circuit downstream from the expansion machine, for condensing the working medium.
In the known waste heat utilization device, the evaporator is coupled by a heat-exchanger to a cooling circuit of the internal combustion engine in order to withdraw thermal energy from the internal combustion engine. In addition, in the known waste heat utilization device the condenser is coupled via a heat exchanger to a refrigeration circuit of an air conditioner in a vehicle equipped with the internal combustion engine in order to dissipate thermal energy from the waste heat utilization circuit. Furthermore, in the known waste heat utilization device a fluid coupling is provided between the refrigerating circuit of the air conditioner and the waste heat utilization circuit.
A heating or cooling device based on a Rankine cyclic process is known from DE 28 18 003 A1 having a main flow circuit for a fluid refrigerant, in which a heat exchanger, which cooperates with a heat source, as a compressor for the fluid refrigerant, a heat exchanger as a condenser for the fluid refrigerant, a pressure reducing valve, a heat exchanger, which preferably cooperates with an air stream to be cooled, as an evaporator, and a return pump for feeding the compressor with the fluid refrigerant, are situated one after the other in the flow direction, the compressor being formed from at least two heat exchangers for heat exchange between the fluid refrigerant and the heat source, and switchover devices are provided for feeding the condenser by the two heat exchangers in alternation, and at the same time the pump feeds the heat exchanger which at that time is not feeding the condenser, by means of a switchover sequence that is adapted to the alternating function of the heat exchangers. The return pump feeds the particular heat exchanger which is connected at that time, preferably with fluid refrigerant in the vaporous physical state. In the known heating or cooling device, the switchover devices are provided primarily to ensure that the heat source cooperates only with the heat exchanger(s) of the thermal compressor which is/are filled with fluid refrigerant at that time. To increase the uniformity of the function of the known heating or cooling device, a storage cylinder is provided directly downstream from the condenser, the storage cylinder continuing to, feed the main flow circuit, i.e., the pressure reducing valve and the evaporator connected downstream therefrom, even during time intervals of several seconds' duration in which the heat exchangers are temporarily switched off in the course of the switchover operation.
A waste heat utilization device which operates according to the Rankine cyclic process or according to the Rankine Clausius process is designed for operation at comparatively high temperatures in the working medium, for example at least 200° C. When the internal combustion engine is switched off, this results in cooling of the working medium, which is accompanied by a significant pressure drop. For example, in a rest state in which essentially an ambient temperature is present within the waste heat utilization device, a resting pressure in the working medium, which may be formed by a mixture of 70% H2O and 30% ethanol, for example, may be approximately 30 mbar (absolute). An enormous level of effort is necessary to be able to consistently seal off such low pressures. If this level of effort is avoided, a diffusion of ambient air into the waste heat utilization circuit results in the rest state. On the other hand, if an attempt is made to increase the quantity of the working medium in the waste heat utilization circuit, in hot operation this results in greatly increased pressures, which likewise are controllable only with a comparatively high level of effort.
It is therefore the object of the present invention to provide an improved design for a waste heat utilization device of the type mentioned at the outset, and for an associated operating method, the design being characterized in particular that the level of effort for sealing off for the rest state or the hot operating state is reduced.